The invention relates to a method and apparatus for displaying ordinate-abscissa value pairs on a display device.
For the graphic display of measured values in measuring devices or systems, for example, in spectrum analyzers or network analyzers, display devices with discrete display points—pixel graphics—are used as standard. The resolution of such display devices is restricted because of the limited number of display points in the ordinate direction and abscissa direction. The maximum resolution of such display devices is currently, for example, around 1000*600 display points.
A spectrum analyzer as shown in FIG. 1 comprises, for example, a low-pass filter 1 for frequency limitation of the signal to be displayed, an analog-digital converter 2 for digitizing the signal to be displayed, a Fast Fourier Transformer 3 (FFT) for calculating the discrete Fourier spectral lines by fast Fourier transform, a modulus-former 4 for determining the power spectral lines, a logarithmic amplifier 5 for compressing the power spectral lines scattering over a broad signal range to the display range of the display device, and a display device 6 with discrete display points in the ordinate direction and abscissa direction for the display of the discrete power spectral lines. The power spectrum to be displayed provides a resolution in the abscissa direction at the level of the FFT length NFFT of the FFT transformer 3—typically NFFT=2048—and a resolution in the ordinate direction at the level of the word width of the logarithmic amplifier 5—typically 216=56636 level steps. Since the resolution of the measured values to be displayed is greater in both the abscissa direction and also the ordinate direction than the resolution of the display device 6, the resolution of the measured values to be displayed must be reduced before implementing the display of the measured values on the display device 6.
Reducing the resolution of the measured values to be displayed in the abscissa direction disadvantageously leads to a loss of information of the measured values to be displayed in the ordinate direction. Strong fluctuations of the measured values to be displayed over a relatively large value range in the ordinate direction accordingly lead to an unacceptable error in accuracy, especially in the case of real-time data collection and display.
A method for displaying ordinate-abscissa value pairs on a display device which provides a lower resolution in the ordinate direction and abscissa direction than the resolution of the ordinate-abscissa value pairs is known from DE 2006 047 994 A1. To minimize the loss of information in the display of the ordinate-abscissa value pairs resulting from a reduced resolution of the display device, abscissa ranges are defined in each case which extend from an abscissa-range limit on the left, at half the spacing between the respective abscissa value and the respective, adjacent abscissa value on the left of the display device up to, respectively, an abscissa-range limit on the right, at half the spacing between the respective abscissa value and the adjacent abscissa value on the right. Interpolated ordinate values are calculated by interpolation at the individual abscissa-range limits. For each abscissa range, a maximum and a minimum ordinate value is determined in each case from all of the ordinate values disposed within the abscissa range with the addition of the interpolated ordinate values at the abscissa-range limits. As shown in FIG. 2, within each abscissa range, the display device described in DE 10 2006 047 994 A1 contains an area, in each case, between the two abscissa-range limits and the determined maximum and minimum ordinate value.
The method described in DE 10 2006 047 994 A1 does not generate any frequency of distribution values in a histogram display. A triggering in response to frequencies of distribution is therefore not possible. Moreover, such a signal evaluation and display is not suitable for signals with a given background noise (noise carpet), because the display of areas by comparison with a display of accumulations of points is a non-typical and unnatural form of display for background noise. Moreover, as a result of the method, in the histogram display of a sinusoidal base signal with superposed background noise, as shown in FIG. 3, the maximum for the frequency of distribution of the background noise is displaced downwards by a few decibels by comparison with a correct display.
In a dot display, as shown in FIG. 4, only the individual measured ordinate values at the individual abscissa values are registered without calculation of additional interpolated ordinate values and converted to ordinate-abscissa value pairs in the resolution of the display device. Accordingly, in a histogram display with constant spectral components with steep edges as shown in FIG. 5, for example, in the case of a sinusoidal signal component occurring as a spectral line, only unconnected collections of dots are displayed, which are more difficult to identify for the observer than interpolated signal characteristics.
What is needed, therefore, is an approach for displaying ordinate-abscissa value pairs on a display device with a lower resolution in the abscissa direction and in the ordinate direction by comparison with the resolution of the ordinate-abscissa value pairs, which, especially in the case of a histogram display, does not lead to a curve characteristic which is error-laden and/or difficult to identify.